Mammalian interferons are valuable proteins useful in protecting and treating animals and humans from viral and other diseases, through the myriad actions of interferon (IFN). Marcus, Encyclopedia of Virology, 2:733-739 (1994); Krown et al., Encyclopedia of Virology, 2:739-745 (1994). The Food and Drug Administration has approved several uses of human IFN. Comparable studies with chickens and other avian species have been limited by the availability of chicken and avian IFN. Induction of avian interferon by virus has been successful in primary chick embryo cells "aged" in vitro, with yields of more than 100,000 units of IFN per 10.sup.7 cells (Sekellick and Marcus, Methods in Enzymology, 119:115-125 (1986)), and chicken interferon (ChIFN) has been shown specifically to protect chicken cells against the lethal action of several viruses (Marcus and Sekellick, Virology, 69:378-393 (1976); Marcus et al., Journal of General Virology, 64:2419-1431 (1983); Portnoy and Marigan, Journal of Infectious Diseases, 124:545-552 (1971); Vengris and Mare, Avian Diseases, 17:755-767 (1973)).
Virus diseases represent a continuous threat to the poultry industry. For example, the "Foreign Animal Disease Report," USDA, 1994, reported in 1983/1984 that an outbreak of the highly pathogenic H5N2 avian influenza virus in Pennsylvania, Maryland, New Jersey and Virginia resulted in the death of 17 million birds. A less pathogenic strain was isolated on a game farm in Maryland in 1993. The infection led to the depopulation of the flock. Some important parasitic diseases of chickens like that caused by Eimeria may be controllable by interferon through its effects on the immune system. Interferon is gaining increased attention as an antiparasitic agent, (Murray, Journal Interferon Research, 12:319-322 (1992)).
Many factors determine how much interferon is induced by a particular virus. These factors include its origin and passage history, the host cell, incubation conditions and time, and the multiplicity of infection. Stewart, "The Interferon System", 2nd. ed., Vienna:Springer-Verlag, pp 27-57; Marcus, Sekellick and Nichol, Journal of Interferon Research, 12:297-305 (1992).